This invention relates to a device for the temporary interruption of the pressure build-up in a fuel injection pump for internal combustion engines, comprising a pressure relief body which is guided by a guiding part and loaded by a pre-loading force against whose action it will slide up to a given stop under the pressure of the fuel entering from the pressure chamber of the pump, the pressure-loaded area being small in the closed position of the pressure relief body as compared to that in its open position, which body will give access to an expansion space after a given pressure level has been reached, the expansion space being bounded by the pressure relief body and the guiding part, and being depressurized by a separate by-pass line.
The purpose of such temporary interruption of the pressure build-up is a division of the process of injecting fuel into the combustion chamber of an internal combustion engine into a pre-injection phase and a main injection phase, thus influencing the combustion process and reducing combustion noise, above all. As soon as the pressure in the injection system exceeds a certain level determined by the pre-loading force and the pressure-loaded area of the pressure relief body, an expansion space is opened up, usually abruptly, due to the sudden enlargement of the area loaded by pressure, which will lead to a temporary pressure drop in the injection system and a temporary closing of the injection nozzle after its initial opening for pre-injection. When the pressure relief body has reached its maximum displacement the expansion volume will remain constant, and the pressure in the fuel which is constantly being delivered by the injection pump, will rise again, eventually leading to the main injection process.